1. Field of the Invention
The present invention relates to a length and velocity measurement apparatus and more particularly, to a length and velocity measurement apparatus which includes an RF modulated continuous wave (CW) laser in which the distance between the measurement apparatus and a target is measured by counting the periods in an interference pattern created between the amplitude modulation components of respectively the transmitted and reflected signals while the modulation signal is swept from a frequency F.sub.1 to a frequency F.sub.2. The velocity measurements are made at a constant RF modulation frequency, the periodic interference pattern is then induced by the moving target (Doppler effect).
2. Description of the Prior Art
Various apparatus are known for measuring the distance and speed of various objects. Both radio detection and ranging (RADAR) and sound navigation and ranging (SONAR) measurement apparatus are known. Portable radar systems are known to be used for detection and location of relatively large to very large objects at moderate to large distances. Such portable radar systems use a short wavelength in order to use a small antenna. The ability of a radar system to distinguish between neighboring objects is determined by the beam-width of the emitted RF/microwave signal. The beamwidth of the system is determined by the antenna size. In particular, the beamwidth is .apprxeq..lambda./D where .lambda.=wavelength and D=the diameter in the major axis in the antenna aperture. Unfortunately, many portable radar systems, such as police radar systems, have problems with false readings due to the wide beamwidth or sidelobes that illuminate a number of unwanted targets.